RFR: 8277990: NMT: Remove NMT shutdown capability [v2]

[Thomas Stuefe]

On Thu, 2 Dec 2021 18:23:07 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> NMT shutdown functionality is a remnant of its first implementation, which could consume excessive amount of memory, therefore, it needed capability to shut it self down to ensure health of JVM. This is no longer a case for current implementation.
>> 
>> After JDK-8277946, there is no longer a use, so it can be removed.
>> 
>> Test:
>> - [x] hotspot_nmt
>> - [x] tier1 with NMT on
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   tstuefe's comments

Let's ship this, I'm really interested in getting this into JDK 18 before ramp-down on Thursday.

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PR: https://git.openjdk.java.net/jdk/pull/6640